Flyback converters relatively posses the advantages of having simple configuration and lower costs, and have been broadly applied to the apparatuses such as adapters etc. As shown in FIG. 1(a), it is a circuit diagram of a flyback converter in the prior art. In which, the flyback converter includes a transformer T, a switch SW, a diode D and an output capacitor C receiving a DC input voltage Vin and an output voltage Vout. FIG. 1(b) shows a schematic circuit diagram of a flyback converter having a magnetic core (mc) in the prior art. In which, the magnetic core mc has an air gap g, the transformer T includes a primary winding Np and a secondary winding Ns. The operational principles are: 1. a current flows through Np when the switch SW is turned on, the diode D is cut off, and then the energy stores in the transformer T; and 2. the diode D is turned on when the switch SW is turned off, and then the energy is released to the output. But the aforementioned flyback converter has the disadvantages: the energy transmission capability is inferior, the input/output ripples are relatively larger, the utilization ratio of magnetic core is low, and the winding loss is larger (especially the transformer's air gap fringing loss), thus the flyback converter is not preferred in the high power applications. The flyback converter can be viewed as the simplest magnetic integrated circuit/structure of the isolated converters. When the trend is increasing the output power and the power density, the flyback converter no longer fits in the requirements for the development of power sources.
Therefore, the interleaved flyback converters having the advantages of possessing lower input/output ripples, increasing the energy transmitting capability and enhancing the output power are proposed and employed. As shown in FIG. 2(a), it is a circuit diagram of an interleaved flyback converter in the prior art, includes a first transformer T1 (the polarity of the first terminal of its primary winding Np1 is the same as the polarity of the first terminal of its secondary winding Ns1), a second transformer T2 (the polarity of the first terminal of its primary winding Np2 is also the same as the polarity of the first terminal of its secondary winding Ns2), a first switch SW1, a second switch SW2, a first diode D1, a second diode D2 and an output capacitor C, the converter is used to receive a DC input voltage Vin and generate an output voltage Vout, the primary and secondary windings Np1 and Ns1 of the first transformer T1, and the primary and secondary windings Np2 and Ns2 of the second transformer T2 are shown. In FIG. 2(b), it is a circuit diagram of an interleaved flyback converter having two magnetic cores (mc1 and mc2) in the prior art. In which, is1 is the current flowing through the first secondary winding Ns1, is2 is the current flowing through the second secondary winding Ns2, ip1 is the current flowing through the first primary winding Np1, ip2 is the current flowing through the second primary winding Np2, the first switch SW1 has a driving voltage Vg1, the second switch has a driving voltage Vg2, and the remaining part is the same as that of FIG. 2(a). Please refer to FIG. 3, which is a waveform diagram of the voltages (Vg1 and Vg2) across the first and second switches (SW1 and SW2), currents (ip1 and ip2) flowing through the primary windings (Np1 and Np2), currents (is1 and is2) flowing through the secondary windings (Ns1 and Ns2), and the converter's output current (iout) of the interleaved flyback converter as shown in FIG. 2(b) respectively.
For the above-mentioned interleaved flyback converters, the current ripples on each of the channels are not improved, and this becomes an important obstacle for increasing the efficiency and decreasing the volume of the power sources. When the changing trend is increasing the density and decreasing the operating voltages of electronic apparatuses in the IC, it is necessary to study how to decrease the current ripples on each channel of the aforementioned interleaved flyback converters. And, the light load loss of the electronic apparatuses such as the adapters is also one of the problems to be solved by the present invention.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the applicant finally conceived a magnetic integrated circuit for a multiphase interleaved flyback converter and a controlling method thereof.